Recording - February 2015 - 25

In the 1960s, British engineer Rupert
Neve designed his first solid state mixing
console, with transformers at the input and
output of every stage and transistor circuitry
in between. Like earlier tube equipment, this
console operated in Class A. A tube or transistor can only handle current in one direction, so the signal voltage must stay between
0 and some other, usually higher, voltage.

This is class A. In Class AB the signal swings
from positive to negative using two tubes or
transistors, one handling the positive and
the other handling the negative swing. (See
Figure 4.) Class A eats more power and
generates lots of heat because the circuit is
always passing current. Class AB circuits
run cooler and eat less power, but suffer
from a bit of crossover distortion at the point
where the signal switches between devices.
Class AB does not necessarily sound inferior, but a well-designed Class A circuit can
claim lack of crossover distortion as one of
its sonic merits.
The best challenge to the "tubes are better" line is to just say, "Neve." Neve circuits
exhibit a significant level of delicious harmonic distortion, mostly from the Carnhill
transformers used. You can hear it on thousands of hit records from the 1970s up to the
present day! Check out Dave Grohl's documentary Sound City. Thank me later.
EQ
After the mic preamplifier comes the
equalization circuit. The REDD consoles
had interchangeable EQ units labelled
"Classic" and "Pop" to be used appropriately-a very British attitude, what?
Separate boost and cut knobs for lows and
highs provided shelving response except
for the "Pop" high boost: a peaking
response around 5 kHz. Introduced in

1951, the American Pultec EQP-1 program
equalizer had a transformer input followed
by passive equalization circuitry (no power
supply in the EQ section), feeding an interstage transformer to a Class AB tube gain
makeup circuit and output transformer.
The standalone EQP-1A was intended mainly for broadcast and vinyl mastering. It had
separate high and low boost and cut knobs
with click-stop selectable corner frequencies.
There was a variable "bandwidth" control for
the high boost, but the curves produced were
broad by today's standards. The EQP-1
sounds warm and punchy, with an uncanny
high-end smoothness. Many engineers run
everything through an EQP-1, because it
sounds awesome... even with the EQ flat!
The early Neve 1073 EQ module had
high and low shelving click-stop corner frequency selection and a peaking midrange
band. The fixed bandwidth and center frequency of each click stop were selected by
the golden ears of Mr. Neve himself. The later
1081 EQ module (see Figure 5) added a second mid section, a Hi Q (narrow bandwidth)
switch for the mid bands, and high and low
pass filters. The Neve is difficult to describe
because there is noticeable warmth but also
a slightly more aggressive upper mid character with that very detailed midrange. To me
Neve sounds present, lively, and snappy-it
sounds fantastic before you even touch the
knobs!

http://www.greatriverelectronics.com

Recording - February 2015

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